Joerg Kretschmer, who was last week found guilty of involuntary manslaughter and handed down a 21-month suspended sentence for enabling his 17-year old son to go on a shooting rampage in 2009, has appealed the verdict.

Kretschmer was convicted of negligent manslaughter as he failed to keep his 9mm Beretta pistol secure and away from the reach of his son, Tim. The failure had deadly consequences - Tim went on a shooting rampage at the Albertville high school in Winnenden, killing 15 people, before training the gun on himself on March 11, 2009. Nine of Tim's victims were fellow students at his school and three were teachers. Of the remaining three, one worked at the local psychiatric hospital and two were members of the public in nearby Wendlingen.

During the trial, the prosecutors said Kretschmer, a shooting club member who owned 15 guns, had 14 of his guns stored away in a safe as required by law but kept the pistol, which Tim used, in a linen cupboard in his bedroom, hidden under some jumpers.

A court in Stuttgart court had held that the 52-year-old businessman had failed to keep his registered pistol and ammunition locked away from his son, who had shown signs of manic depression prior to the lethal rampage.

Weapons and ammunition were not separated sufficiently, Judge Reiner Skujat said.

The shooting incident at Winnenden wouldn't have happened without the utter mistake of the accused in his storage of the firearm, the judge said, convicting Kretschmer on 15 counts of homicide by negligence and 14 counts of causing bodily harm by negligence, as well as charges under gun safety laws.

However, Kretschmer's lawyer said they would appeal the verdict as it was not in line with the original charges, which merely related to gun safety.